1. Field of the Invention
This invention relates to a prosthesis construction wherein the stem of the prosthesis is provided with means to centralise its proximal end in a bone socket.
2. Description of Prior Art
According to the present invention in a prosthesis provided with a stem for fixation with cement in a bone socket, the proximal portion of the stem is provided with a number of shaped projections which are dimensioned to contact the inner wall of the bone socket and to act to guide the proximal end of the stem therein. Such a stem as shown in U.S. Pat. Nos. 5,116,380 and 5,163,963.
In a preferred construction said projections are fastened to said stem by detachable attachment means which can release if there is subsequent downward movement of the stem in the bone socket after initial implantation.
Said projections may be of teardrop shape facing towards the proximal or distal ends of the stem.
The attachment means can be provided by a releasable adhesive, shear pins or by relying upon the relative adhesion between a smooth surface on the projection and a smooth surface on the stem.
The projections can be made of any convenient material, for example polymethylmethacrylate (PMMA).
In one preferred construction the projections are located on the corners of a stem which is of triangular, square or rectangular cross-section.